Double sided discs are assumed to be single step and flip-sided, but the\ sidedness and stepping can be changed by function 1, requesting the\ \"Other\" format types.\
Sidedness of three kinds are recognised:\
The table below may (or may not) make this clearer. If in doubt, use Flip\
sides, which is the fastest and commonest format. If you are trying to\
read a strange disc and Flip sides produces nonsense, then try Up and\
Over A, which is much more common than B.\
| Sidedness | Logical track no | \
Physical track no | Side |
|---|---|---|---|
| Flip sides | \0 | 0 | 0 |
| 1 | 0 | 1 | |
| 2 | 1 | 0 | |
| 3 | 1 | 1 | |
| 159 | 80 | 1 | |
| Up and Over A | \0 | 0 | 0 |
| 1 | 1 | 0 | |
| 79 | 79 | 0 | |
| 80 | 79 | 1 | |
| 159 | 0 | 0 | |
| Up and Over B | \0 | 0 | 0 |
| 79 | 79 | 0 | |
| 80 | 0 | 1 | |
| 159 | 79 | 0 |
Sidedness and stepping are recorded at &BE3A and &BE3D for drive A & B\ respectively. They are set to the default values of 0 and &8F on\ initialisation and can be changed by poking new values. The byte value is\ worked out as follows (where x is any bit value):\
One powerful facility of RAMDOS is the ability to read or format tracks\ whose logical track numbers are different from their physical track\ numbers. This allows the creation of protected discs which can only be\ read with RAMDOS. The physical track number is position of the track on\ the disc (0-39 or 0-79), and the logical track number is the number\ encoded into the sectors when formatting. The offset is the difference\ between them. This offset must be poked into &BE39 for drive A and &BE3?\ [here the original documentation is unclear - DC]\ for drive B. The default value is zero, which allows the reading of all\ normal formats.\
The formats D10,D20,D40 and D80 hold more data because they use 10\ sectors per track, instead of the normal 9.\ ");